I've decided to let yesterday's question sit for a day, so there's more time for feedback. In the meantime, I'm going to revisit an old subject: how AI competitors can augment human competition.
AI can be more conducive to player strategy than player opponents. Strategy is only possible to the extent that things can be predicted. If you can't foresee something, then you can't plan for it. Of course, sometimes predictability includes the lack thereof (you expect that something unexpected will occur, though you don't know exactly what).
Playing against a particular "personality" many times allows the player to gradually adapt, to develop a strategy over the course of multiple play-sessions. In multiplayer, human personalities are often unstable... meaning that players have fluid styles (due to mood, learning, or battle scenarios), they make impulsive decisions, etc. There's also frequent personality turnover, meaning that you're constantly playing new competitors and there are long intermissions between battles against any one competitor.
AI in the form of "multiplayer" bots serve two main functions. First, they prepare players for facing particular strategies and scenarios. There's wide discrepancy between how much time different players need for this. Second, they can offer a fun alternative to unpredictable nature of human beings. Even players who enjoy the challenge and dynamics of human competition sometimes want a change of pace, a different experience. AI can act as a nice balance and prevent players from burning out.
There are other potential uses, but I just wanted to emphasize the value of AI for supporting strategic gameplay. Don't think of bots as an alternative to players. Interaction with bots can aid interaction between players.
And don't think that AI in a single-player campaign acts in the same way.